The development of a functional nervous system requires the correct specification and precise organization of a large number of neural cell types. These cell types fall into two major categories: neurons and glia. The goal of the proposed research is to understand the mechanisms by which neural progenitor cells acquire glial cell fates as opposed to neuronal fates, and how glial cell differentiation is accomplished. To achieve this goal we are investigating the glial cells missing (gcm) gene, a master regulator of glial cell fate in Drosophila. gcm encodes a novel DNA-binding transcription factor that is required for the development of nearly all glia in Drosophila. In the presence of GCM protein, neural cells develop into glia, while in its absence they become neurons. Several gcm homologs have been identified in mammals, including humans, and they have been shown to have conserved biochemical properties. Their exact role in development is not yet clear. Modern biology has demonstrated that molecular genetic pathways have been conserved throughout evolution. It is highly likely that the mechanism of action mammalian gcm homologs will be similar to those observed in Drosophila. We believe that the proposed research will be directly relevant to understanding how Gcm family genes control cell fate determination in humans and thereby contribute to gaining new tools in the combat of diseases and injuries of the nervous system. We propose to continue the molecular genetic analysis of gcm to understand the mechanisms controlling the glia/neuron cell fate choice in Drosophila. We operate under the hypothesis that the precise regulation of gcm must occur to ensure glial cell determination, and propose several approaches to identify the genetic machinery regulating gcm. gcm is expressed transiently - it can therefore only initiate, but not maintain, the differentiated glial cell state. The differentiated glial state must therefore be determined through the activity of downstream genes. We aim to identify these downstream genes, and propose several approaches to understand the means by which glial cell differentiation is achieved.